This invention relates to apparatus for measuring operating parameters of a high voltage power conductor. More particularly, it relates to radio transmitting sensors which can be permanently mounted on an overhead power transmission line or portable sensors which are connected to a transmission line at arbitrary points for short periods. The permanently mounted sensors normally derive their operating power through electromagnetic induction using the magnetic field generated as a result of current flowing through the transmission line conductor. Transmission line sensors of the above type are disclosed in the United States Patent of Howard R. Stillwell and Roosevelt A. Fernandes entitled Transponder Unit for Measuring Temperature and Current on Live Transmission Lines, U.S. Pat. No. 4,384,289, issued May 17, 1983, which patent is incorporated herein by reference. Various other power line sensors, disclosed in the prior art, have been proposed for dynamic line rating of electrical power transmission lines. For examples, see U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810, and 4,268,818.
The power line sensors available in the prior art measure quantities associated with the operation of the overhead line such as voltage on the conductor, current flow in the conductor, conductor temperature and ambient temperature. These measured parameters are transmitted by the sensor to a local ground station. Data from the various ground stations is then transmitted to a central control station where the information is analyzed. Based on this analysis, the entire power system is controlled with power being supplied to the various transmission lines in accordance with their measured parameters.
The compact toroidal-shaped sensors, disclosed in U.S. Pat. No. 4,384,289 and in the prior copending applications of Fernandes et al. contain the sensor electronics, power supply and transmitter circuits, and hardware for attaching the sensors to the transmission lines. These sensors generally derive their operating power from current flowing in the conductor but can also be operated by a battery when the line current is at a minimal or zero level. The sensor module power supply operates the electronics to process the measured parameters and the transmitter to transmit the processed values. These processed values are normally transmitted by antennas which tend to be highly directional such as a dipole antenna or patch antenna attached to the exterior of the sensor housing. These antennas are functional in a limited frquency range and are tuned to the particular operating frequency of the transmitter.
The present invention overcomes the disadvantages of the antenna apparatus used in prior systems by utilizing both the toroidal housing of the sensor module and the transmission line conductor itself to radiate the radio frequency signals from the transmitter. An impedance matching network is connected between the output of the transmitter and the housing of the sensor module. This network matches the operating frequency of the transmitter, which in the preferred embodiment is 950 MHz, to the impedance of the housing of the toroidal sensor module. The broadband tuning effect of the impedance matching network matches the resonant characteristics of the housing to the operating frequency of the transmitter. The housing of the sensor module, in combination with the impedance matching network, acts tuned as a resonating choke which permits the transmitter to drive the transmission line against the plane of the housing. Metal rings separated by an insulation layer in the module housing function to tightly capacitively couple the module hub to the transmission line conductor at high frequencies. The transmission line conductor acts as a nonresonant wire antenna which functions to radiate the transmitter signals into space. The impedance matching network, the toroidal housing of the module, and the line conductor provide a broadband antenna system with desirable gain and directivity characteristics for transmitting the processed line values to a remote ground station.
It is therefore an object of the present invention to provide an improved antenna system for use in a power transmission line monitoring system.
Another object is to provide an antenna with a desirable radiation pattern with improved gain and directivity characteristics for transmitting signals to a remote ground station.
A further object of the invention is to provide an antenna system with an improved impedance matching network providing broadband capabilities.
Another object of the invention is to provide an antenna system which utilizes the toroidal housing of a transmission line sensor as a resonating choke to drive the hub of the housing to radiate high frequency signals.
Still another object of the invention is to utilize the transmission line conductor in cooperation with the sensor module housing as a line antenna for radiating signals to a remote station.
These and other objects and advantages of the invention will be apparent from the following detailed description and drawings.